One of the major Hanbali authorities and the author of the profound and voluminous book on Law, al-Mughni, which became popular amongst researchers from all juristic backgrounds. He was also an authority on Hanbali doctrine and a passionate opponent of the Ash’arites, but that did not prevent him from joining the military campaign of Salah al-Din al-Ayyubi, who was an Ash’ari, against the Crusaders in Palestine.